Control device, electro-optical device, driving method for electro-optical device and electronic apparatus

ABSTRACT

A control device for a display unit that includes pixels each having display elements is disclosed. The control device comprising a control unit counting sections where pixels with different gradations are placed next to each other in a predetermined region among an image to be displayed on the display unit. The control unit outputs an instruction to execute a refresh drive in the predetermined region when an integrated value of the sections exceeds a predetermined value.

BACKGROUND

1. Technical Field

The present invention relates to technologies for reducing afterimagesgenerated at outlines of displayed images.

2. Related Art

An electro-optical device using the memory-property of display elementssuch as electrophoretic elements, electronic powder-particle elements,and cholestric liquid crystal elements has been known. For the sake ofsimplicity of the description, let us assume that the display elementsdisplay binary values, for example, white color and black color. Forexample, when the entire pixels are switched to white color to performan all-white display, a differential drive is executed. The differentialdrive uses the memory property of the display elements, in whichwhite-displayed pixels in a preceding image are not driven, andblack-displayed pixels other than white color in the preceding image aredriven to be switched to white color (see, for example,JP-A-2007-206267).

However, in the differential drive, when the entire pixels are switchedto white color, there is a problem in that an afterimage would likely begenerated in the vicinity of a boundary between those of the pixels thatcontinue to be white and those of the pixels that are switched fromblack to white. A similar afterimage would also likely be generated,when the entire pixels are switched to black color, in the vicinity of aboundary between those of the pixels that continue to be black and thoseof the pixels that are switched from white to black. Such an afterimageappears along an outline of an image before switching, and therefore maybe referred to as an outline afterimage.

SUMMARY

The invention has been made in view of the circumstance described above,and it is an object of the invention to provide a technology thatreduces such afterimages as described above, and enables high-qualitydisplay.

It is thought that the afterimage described above appears because, forexample, when a white pixel and a black pixel are placed next to eachother, the electric field on one of the white pixel and the black pixelinfluences the other pixel, and the influence remains even after both ofthe pixels are switched to the same color. Accordingly, in order toerase the afterimage, a refresh drive may be conducted to remove theremaining influence. However, this type of refresh drive wastes power.In view of the fact that one of the major characteristics of the displayelement having memory property resides in low power consumption, anystructure that frequently executes such refresh drive, which goesagainst the characteristic, is not preferable.

In accordance with an aspect of the invention, a control device for adisplay unit that includes pixels each having display elements isconfigure to output an instruction to execute a refresh drive in apredetermined region among an image to be displayed on the display unitwhen an integrated value that counts sections where pixels withdifferent gradations are placed next to each other in the predeterminedregion exceeds a predetermined value.

In accordance with another aspect of the invention, when the integratedvalue exceeds the predetermined value, it is preferable that, afterinstructing to rewrite the entire pixels included in the predeterminedregion to a single gradation, rewriting pixels, among the pixelsincluded in the predetermined region, with a gradation different fromthe single gradation may be instructed.

In the control device described above, when the integrated value equalsto the predetermined value or less, rewriting of pixels to be changed inthe predetermined region may be instructed. By the execution of thedifferential drive, wasteful power consumption can be suppressed.

In accordance with an another aspect of the invention, the controldevice described above may preferably include an extraction functionthat extracts sections where pixels with different gradations are placednext to each other in the predetermined region, a counting function thatcounts the sections extracted by the extraction function, and a judgingfunction that judges as to whether an integrated value provided by thecounting function exceeds the predetermined value.

Here, the extraction function may be configured to extract sectionswhere pixels with different gradations are placed next to each other forthe first time, after the last display of the pixels with the singlegradation.

In accordance with another aspect of the invention, a control device fora display unit that includes pixels each having display elements may beconfigured to output an instruction to execute a refresh drive in apredetermined region among an image to be displayed on the display unit,when an integrated value that counts sections where pixels withdifferent gradations placed next to each other change to a singlegradation in the predetermined region exceeds a predetermined value.This configuration can improve the situation in which an afterimage thatis not so conspicuous is reset.

In the control device described above, the predetermined region may becomposed of all or a part of the plurality of pixels in the displayunit. In particular, when the predetermined region is composed of a partof the pixels, afterimages can be made inconspicuous in regions wheredisplay contents are frequently changed.

It is preferable that the refresh drive may include rewriting all of thepixels included in the predetermined region to a single gradation.

It is noted that the invention is applicable not only to a controldevice, but also to an electro-optical device, a method for driving theelectro-optical device, and an electronic apparatus having theelectro-optical device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the structure of an electro-opticaldevice in accordance with a first embodiment of the invention.

FIG. 2 is a diagram showing an equivalent circuit of pixels in a displayunit.

FIGS. 3A and 3B are views for explaining operations of electrophoreticelements.

FIG. 4 is a flow chart showing operations of the electro-optical devicein accordance with the first embodiment.

FIG. 5 is a flow chart showing an outline detection process inaccordance with the first embodiment.

FIG. 6 is a diagram for explaining shifting of the target pixel in afirst VRAM.

FIGS. 7A-7H are diagrams for explaining comparison with the target pixelin the first embodiment.

FIGS. 8A-8C are diagrams showing, as an example, changes in a displayimage on the electro-optical device in accordance with the firstembodiment.

FIGS. 9A-9G are diagrams showing an example of the refresh drive inaccordance with the first embodiment.

FIGS. 10A-10C are diagrams showing an example of the differentialdriving in accordance with the first embodiment.

FIG. 11 is a flow chart showing an outline detection process inaccordance with a second embodiment.

FIG. 12 is a diagram for explaining boundary flags in accordance withthe second embodiment.

FIGS. 13A-13D are diagrams for explaining comparison with the targetpixel in accordance with the second embodiment.

FIG. 14 is a flow chart showing an outline detection process inaccordance with a third embodiment.

FIG. 15 is a flow chart showing an outline detection process inaccordance with the third embodiment.

FIGS. 16A-13H are diagrams for explaining comparison with the targetpixel in accordance with the third embodiment.

FIG. 17 is a view showing a display example in accordance with anapplication example.

FIGS. 18A and 18B are views showing electronic apparatuses that use anelectro-optical device in accordance with embodiments of the invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS First Embodiment

Embodiments of the invention will be described below with reference tothe accompanying drawings. FIG. 1 is a block diagram showing anelectrical configuration of an electro-optical device 1 in accordancewith a first embodiment. As shown in FIG. 1, the electro-optical device1 includes a display unit 10, a first VRAM 51, a second VRAM 52 and acontroller 60.

The display unit 10 includes a plurality of scanning lines 112 providedalong a row (X) direction, and a plurality of data lines 114 providedalong a column (Y) direction in a manner to be electrically insulatedfrom the scanning lines 112. Further, pixels 20 are provided atpositions corresponding to intersections between the scanning lines 112and the data lines 114. When the number of rows of the scanning lines112 is “m” and the number of columns of the data lines 114 is “n,” forconvenience sake, the pixels 20 form a display region 100 in which mrows in the vertical direction×n columns in the horizontal direction arearranged in a matrix.

A scanning line drive circuit 130 selects one of the m rows of scanninglines 112 according to the control by the controller 60, supplies a high(High) level signal to the selected scanning line 112, and supplies alow (Low) level signal to the other scanning lines 112. A data linedrive circuit 140 drives the data lines 114 according to displaycontents for the pixels 20 for one row located in the selected scanningline 112.

The first VRAM 51 and the second VRAM 52 are video RAMs each havingstorage regions respectively corresponding to the pixels arranged in mrows×n columns, and accessed (read and written) by the controller 60. Asdiscussed later, when the display content of the display unit 10 ischanged, an image after the change is stored in the first VRAM 51, andan image prior to the change is stored in the second VRAM 52. Therefore,by comparing the content stored in the first VRAM 51 with the contentstored in the second VRAM 52, pixels whose display is to be changed (tobe rewritten) can be discriminated from pixels that do not requirerewriting.

The controller (control device) 60 includes a general control unit 62, atemporary storage unit 64, a refresh drive control unit 66, and adifferential drive control unit 68. The general control unit 62 controlseach of the units, and executes a program to perform various functionsto be discussed below, such as, an extraction function, a countingfunction, and a judging function. The temporary storage unit 64 is a RAMand temporarily stores variables to be used in operations to bediscussed below. The refresh drive control unit 66 controls the scanningline drive circuit 130 and the data line drive circuit 140 to drive theentire pixels 20 by refresh drive, when a condition to be discussedbelow is met when an image to be displayed on the display unit 10 ischanged. The differential drive control unit 68 controls the scanningline drive circuit 130 and the data line drive circuit 140 to drive onlythose of the pixels 20 which are changed, when a condition to bedescribed below is not met when an image to be displayed on the displayunit 10 is changed. It is noted that the controller 60 connects to ahost device (e.g., CPU) whose illustration is omitted in FIG. 1, andregulates an image to be displayed on the display unit 10.

FIG. 2 is a diagram showing an equivalent circuit of the pixels 20 inthe display unit 10, which shows a configuration of four (2×2) pixels intotal corresponding to intersections between an i^(-th) row and anadjacent (i+1)^(-th) row on the lower side, and a j^(-th) column and anadjacent (j+1)^(-th) column on the right side. It is noted that i and(i+1) are signs that generally indicate rows of the arranged pixels 20,and are integers between 1 and m, and j and (j+1) are signs thatgenerally indicate columns of the arranged pixels 20, and are integersbetween 1 and n.

As shown in FIG. 2, each of the pixels 20 includes an n-channel thinfilm transistor (hereafter simply abbreviated as a TFT) 22, a displayelement 30 and an auxiliary capacitor 40. As the pixels 20 have the sameconfiguration, details thereof will be descried using a pixel 20 locatedat an intersection between the i^(-th) row and the j^(-th) column asrepresentative. In the pixel 20 at the i^(-th) row and the j^(-th)column, the TFT 22 has a gate electrode connected to the i^(-th)scanning line 112, a source electrode connected to the j^(-th) data line114, and a drain electrode connected to a pixel electrode 32 that is oneend of the display element 30 and to one end of the auxiliary capacitor40.

Although not particularly shown, the display unit 10 includes an elementsubstrate with the pixel electrodes 32 formed thereon, a countersubstrate with a common electrode 36 formed thereon, and anelectrophoretic layer 34 having dielectric property which is heldbetween the element substrate and the counter substrate. Therefore, thedisplay element 30, as viewed in the equivalent circuit, defines acapacitance in which the electrophoretic layer 34 is held between thepixel electrode 32 and the common electrode 36. The display element 30retains (stores) a voltage between the two electrodes, and performs adisplay to be described below according to an electric field directiongenerated by the retained voltage. The auxiliary capacitor 40 has aconfiguration in which a dielectric layer is held between a pair ofelectrodes formed on the side of the element substrate. An electrode onthe other end of the auxiliary capacitance 40 is commonly connected to acommon capacitance line 132 across each of the pixels. Also, an externalcircuit (not shown) applies a voltage Com to the common electrode 36,and applies a voltage Vss to the capacitance line 132. However, for thesake of simplicity of explanation, it is assumed that the voltage Comand the voltage Vss are both set at a grounding voltage that is areference voltage (0V).

Display operations of the display element 30 are described withreference to FIGS. 3A and 3B. The electrophoretic layer 34 is a layer inwhich plural microcapsules 35 are fixed between the pixel electrode 32formed on the element substrate and the common electrode 36 formed onthe counter substrate. Each of the microcapsules 35 includes two kindsof electrophoretic particles moveably dispersed in a dispersion medium34 e. The two kinds of electrophoretic particles are white particles 34w that are negatively charged, and black particles 34 b that arepositively charged. With this configuration, as shown in FIG. 3A, when avoltage Corn, for example, 0V is applied to the common electrode 36, anda voltage, for example, −15V is applied to the pixel electrode 32,thereby maintaining the common electrode 36 relatively at a higherpotential than the pixel electrode 32, the white particles 43 w aredrawn toward the common electrode 36 and the black particles 34 b aredrawn toward the pixel electrode 32. When a conductive layer havingtransparency such as ITO (Indium Tin Oxide) is used as the commonelectrode 36, and the counter substrate is configured to be transparent,the pixels 20 can be visually recognized as white as observed from theside of the common electrode 36. On the other hand, as shown in FIG. 3B,when a voltage of 0V is applied to the common electrode 36, and avoltage of, for example, +15V is applied to the pixel electrode 32,thereby maintaining the common electrode 36 relatively at a lowerpotential than the pixel electrode 32, the black particles 43 b aredrawn toward the common electrode 36 and the white particles 34 w aredrawn toward the pixel electrode 32. As a result, the pixels 20 can bevisually recognized as black as observed from the side of the commonelectrode 36.

The electrophoretic layer 34 is configured in a manner that themicrocapsules 35 filled with the dispersion medium 34 e and containingcharged particles dispersed therein are placed in a gap between twosubstrates (two electrodes). The electrophoretic layer 34 may beconfigured with charged electronic powder particles enclosed withoutmicrocapsules between the two substrates, or with cholestric liquidcrystal enclosed between the two substrates. In any of theconfigurations, a voltage between the pixel electrode 32 and the commonelectrode 36 is retained, and the display is performed according to theelectric field direction generated by the retained voltage.

Next, an outline of the operation of the electro-optical device 1 willbe described. FIG. 4 is a flow chart showing processes (main flow)executed when the display content is changed. These processes areexecuted when the controller 60 receives an instruction to change thedisplay content from the CPU that is the host system, and receives asupply of image data after change. First, in step Sa1, the generalcontrol unit 62 of the controller 60 reads image data stored in thefirst VRAM 51, and copies the image data onto the second VRAM 52. Next,in step Sat, the general control unit 62 stores the supplied image dataafter change in the first VRAM 51.

Then, in step Sa3, the general control unit 62 judges as to whether ornot a variable Count exceeds a threshold value Th1. The variable Countis incremented by “1” at each occurrence of a white pixel and a blackpixel being located next to each other in the vertical direction or thehorizontal direction in the display content stored in the first VRAM 51,and reset to zero when a refresh drive is executed. Accordingly, thevariable Count indicates an integrated value of sections in which whitepixels and black pixels are positioned next to one another in thedisplay content of the display unit 10, since the last refresh drive.

As described above, it is thought that an afterimage appears because,when a white pixel and a black pixel are placed next to each other, theelectric field on one of the white pixel and the black pixel influencesthe other pixel, and the influence remains even after both of the pixelsare switched to the same color. Accordingly, if a differential drivewere executed to change the display content in a state in which thevariable Count that indicates the integrated value of occurrences inwhich white pixels and black pixels are placed next to each otherexceeds the threshold value Th1, it is presumed that an afterimage wouldoccur to an extent that cannot be overlooked. Therefore, when it isjudged in step Sa3 that the variable Count exceeds the threshold valueTh1, the general control unit 62 instructs the refresh drive controlunit 66, in step Sa4, to execute a refresh drive. By this, at thedisplay unit 10, an image displayed on the display unit 10 is actuallyrewritten by a refresh drive to be discussed later. Thereafter, in stepSa5, the general control unit 62 resets the variable Count to zero tomake it ready for the next refresh drive.

On the other hand, when the variable Count is less than the thresholdvalue Th1, it is assumed that an afterimage would not be conspicuouseven if a differential drive is executed to change the display content.Therefore, when it is judged in step Sa3 that the variable Count is lessthan the threshold value Th1, the general control unit 62 instructs thedifferential drive control unit 68, in step Sa6, to execute adifferential drive. By this, at the display unit 10, an image displayedon the display unit 10 is actually rewritten by a differential drive tobe discussed later.

After step Sa5 or Sa6, the general control unit 62 accesses the firstVRAM 51 in step Sa7, and executes an outline detection process. Afterexecuting the outline detection process, the general control unit 62stands by until next time it receives an instruction to change thedisplay content from the host device CPU. Therefore, the main flow inFIG. 4 is executed each time the host device CPU issues an instructionto change the display content.

FIG. 5 is a flow chart showing details of the outline extractionprocess. First, in step Sb1, the general control unit 62 sets a targetpixel at the first row and the first column. The target pixel is a pixelthat is expediently targeted for detecting an outline. Morespecifically, as shown in FIG. 6, the target pixel is shifted from the1^(st) row and the 1^(st) column to the 1^(st) row and the n^(-th)column, the 2^(nd) row and the 1^(st) column to the 2^(nd) row and then^(-th) column, the 3^(rd) row and the 1^(st) column to the 3^(rd) rowand the n^(-th) column, . . . , the (m−1)^(-th) row and the 1^(st)column to the (m−1)^(-th) row and the n^(-th) column, through them^(-th) row and 1^(st) column to the m^(-th) row and the n^(-th) columnin this order. In step Sb11, the target pixel is set at the 1^(st) rowand the 1^(st) column as an initial value. In step Sb2, the generalcontrol unit 62 reads the pixel value of the target pixel and the pixelvalue of a next pixel located on the right set among the first VRAM 51,and judges as to whether or not the exclusive OR (Xor) of the two pixelvalues is “1.” Here, the pixel value designates a gradation of thecorresponding pixel, and may be “1” to designate white and “0” todesignate black, in the case of binary values like the presentembodiment.

For this reason, in step Sb2, there are two cases in which the exclusiveOR of the two pixel values is “1.” More specifically, the first case iswhere the pixel value of the target pixel is “1” and the pixel value ofa next pixel on the right is “0” as shown in FIG. 7A, and the secondcase is where the pixel value of the target pixel is “0” and the pixelvalue of a next pixel on the right is “1” as shown in FIG. 7B. In eitherof the cases, the general control unit 62 increments the variable Countby “1” in step Sb3. On the other hand, in step Sb2, there are also twocases where the exclusive OR of the two pixel values is not “1,” inother words, when it is “0.” More specifically, the first case is wherethe pixel value of the target pixel and the pixel value of a next pixelon the right are both “1” as shown in FIG. 7C, and the second case iswhere the pixel value of the target pixel and the pixel value of a nextpixel on the right are both “0” as shown in FIG. 7D. In either of thecases, the general control unit 62 skips an increment process in stepSb3.

In step Sb2, it is judged as to whether or not an outline is formedbetween a target pixel and a pixel on the right. A similar judgmentoperation is also executed for the target pixel and an adjacent pixelbelow the target pixel. This operation is executed in step Sb4. Morespecifically, in the step Sb4, the general control unit 62 reads thepixel value of the target pixel and the pixel value of an adjacent pixellocated below the target pixel, and judges as to whether or not theexclusive OR (Xor) of the two pixel values is “1.”

Here, in step Sb4, there are two cases in which the exclusive OR of thetwo pixel values is “1.” More specifically, the first case is where thepixel value of the target pixel is “1” and the pixel value of anadjacent pixel below is “0” as shown in FIG. 7E, and the second case iswhere the pixel value of the target pixel is “0” and the pixel value ofan adjacent pixel below is “1” as shown in FIG. 7F. In either of thecases, the general control unit 62 increments the variable Count by “1”in step Sb5. On the other hand, in step Sb4, there are also two caseswhere the exclusive OR of the two pixel values is “0.” Morespecifically, the first case is where the pixel value of the targetpixel and the pixel value of an adjacent pixel below are both “1” asshown in FIG. 7G, and the second case is where the pixel value of thetarget pixel and the pixel value of an adjacent pixel below are both “0”as shown in FIG. 7H. In either of the cases, the general control unit 62skips an increment process in step Sb5.

Then, in step Sb6, the general control unit 62 judges as to whether ornot the target pixel at the moment is at the m^(-th) row and the n^(-th)column, in other words, at the last row and the last column. If thejudgment result is “No,” then in step Sb7, the general control unit 62moves the target pixel to a next pixel on the right. If the target pixelis at the right end in the matrix arrangement, in other words, only whenit is at the last n^(-th) column, the target pixel is moved to a pixellocated in the next row below at the first column. Then, the processingreturns to step Sb2. On the other hand, when the judgment result in stepSb6 is “Yes,” it means that the variable Count has been counted forsections where white pixels and black pixels are placed next to eachother in the horizontal direction or the vertical direction, and theoutline detection process ends.

It is noted that no pixel exists on the right side of the pixel in thelast n^(-th) column. Therefore, when the target pixel is at the n^(-th)column, the step Sb2 is not executed, and only the step Sb4 is executed.Similarly, no pixel exists below the last m^(-th) row. Therefore, whenthe target pixel is at the m^(-th) row, the step Sb4 is not executed,and only the step Sb2 is executed. Also, the extraction function toextract an outline is realized by the judgment process in the step Sb2and the step Sb4 shown in FIG. 5, and when the judgment results are“Yes,” the counting function is realized by the process of incrementingthe variable Count. Also, the judgment function is realized by theprocess of judging the variable Count in the step Sa3 in FIG. 4.

Next, more concrete operations of the electro-optical device 1 will bedescribed, using an example in which a display image shown in FIG. 8A ischanged to a display image shown in FIG. 8B. As described above, whenthe variable Count exceeds the threshold value Th1 when a display imageon the display unit 10 is changed, the display image is rewritten byrefresh drive (step Sa4).

Such refresh drive will be described with reference to FIGS. 9A-9G.First, the image before change is shown in FIG. 9A, which is the same asthe image shown in FIG. 8A, and is reflected on the content stored inthe second VRAM 52. Next, the refresh drive control unit 66 controls thescanning line drive circuit 130 and the data line drive circuit 140 suchthat, in the image before rewritten, i.e., the image stored in thesecond VRAM 52, the white pixels are inverted to the black pixels. Morespecifically, the refresh drive control unit 66 controls the scanningline drive circuit 130 to select the scanning lines 112 at the firstrow, the second row, the third row, . . . , the (m−1)^(-th) row and them^(-th) row, in this order. Further, the refresh drive control unit 66controls the data line drive circuit 140, referring to the storedcontent in the second VRAM 52, to apply a voltage of +15 to those of thedata lines 114 including pixels located in the selected scanning line112 whose pixel value is “1,” and apply a voltage of 0V to those of thedata lines 114 including pixels whose pixel value is “0” (in otherwords, to make them to have the same potential as the common electrode36). It is noted that those of the pixels whose pixel value is “0” maybe controlled to have a high impedance state (a floating state) so asnot to be electrically connected to any sections by switching off thecorresponding data lines 114. When selected, the scanning line 112 turnsto a high level, and TFTs whose gate electrodes are connected to theselected scanning line turn on (placed in a conductive state), such thatthe pixel electrodes 32 are placed in a state being electricallyconnected to the data lines. As a result, those of the pixels that areoriginally in white color are inverted to black color due to aninversion of the direction of the electric field. On the other hand,those of the pixels that are originally in black color remain to be inblack color as no electric field is generated. Therefore, by thiscontrol, all of the pixels turn to black color, as indicated in FIG. 9C.In this example, the scanning lines 112 are sequentially selected fromthe first row, but the selection can be skipped for any of the scanninglines 112 having no change.

Next, the refresh drive control unit 66 controls the scanning line drivecircuit 130 and the data line drive circuit 140 such that, this time,all of the pixels are inverted from black color to white color, asindicated in FIG. 9D. More specifically, the refresh drive control unit66 controls the scanning line drive circuit 130 to sequentially selectthe scanning lines 112, and controls the data line drive circuit 140 toapply a voltage of −15V to the data line 114 in each of the columns. Bythis control, this time, all of the pixels turn to white color, asindicated in FIG. 9E.

Then, the refresh drive control unit 66 controls the scanning line drivecircuit 130 and the data line drive circuit 140 to write an image afterrewritten, in other words, pixels to be appeared in black color, asshown in FIG. 9F. More specifically, the refresh drive control unit 66controls the scanning line drive circuit 130 to sequentially select thescanning lines 112, and controls the data line drive circuit 140,referring to the stored content in the first VRAM 51, to apply a voltageof +15 to those of the data lines 114 including pixels located in theselected scanning line 112 whose pixel value is “0,” and apply a voltageof 0V to those of the data lines 114 including pixels whose pixel valueis “1.” As a result, those of the pixels whose pixel electrodes areapplied with a voltage of +15V are inverted to black color due to aninversion of the direction of the electric field. On the other hand,those of the pixels on those of the data lines 114 that are at 0V whenselected maintain white color, as no change is generated in thedirection of the electric field. Therefore, as indicated in FIG. 9G, adisplay state that reflects the stored contents in the first VRAM 51 isobtained.

By the refresh drive, all of the pixels are switched to black color, andthen all of the pixels are switched to white color. Therefore, even whenwhite pixels and black pixels are located next to each other in anoriginal image, and the electric field on one of the pixels influencesthe other of the pixels, such influence can be removed. Then, blackcolor pixels are written anew in the state in which the influence isremoved, such that a correct display, as shown in FIG. 8B or FIG. 9G,can be obtained without generating an outline afterimage shown in FIG.8C.

On the other hand, when the variable Count is less than the thresholdvalue Th1 when a display image on the display unit 10 is changed, thedisplay image is rewritten by differential drive (step Sa6), instead ofrefresh drive.

The differential drive will be described with reference to FIGS.10A-10C. First, an image before change is shown in FIG. 10A, which isthe same as the image shown in FIG. 8A, and is reflected on the storedcontent of the second VRAM 52. The differential drive control unit 68compares images before and after rewriting, and controls the scanningline drive circuit 130 and the data line drive circuit 140 such that, asshown in FIG. 10B, only pixels to be changed are inverted. Morespecifically, the differential drive control unit 68 controls thescanning line drive circuit 130 to select the scanning lines 112 at the1^(st) row, the 2^(nd) row, the 3^(rd) row, . . . , the (m−1)^(-th) rowand the m^(-th) row, in this order. Further, the differential drivecontrol unit 68 refers to the first VRAM 51 and the second VRAM 52, andcontrols the data line drive circuit 140 to apply a voltage of −15V tothose of the data lines 114 including pixels located in the selectedscanning line 112 whose pixel value changes from “0” to “1,” apply avoltage of +15V to those of the data lines 114 including pixels whosepixel value changes from “1” to “0,” and apply a voltage of 0V to thoseof the data lines including pixels whose pixel value does not change. Asa result, those of the pixels whose pixel electrodes are applied with avoltage of −15V or +15V are inverted in color due to an inversion of thedirection of the electric field. On the other hand, those of the pixelswhose pixel electrodes are applied with a voltage of 0V maintain theoriginal state as no change is generated. Therefore, as indicated inFIG. 10C, a display state that reflects the stored contents in the firstVRAM 51 is obtained.

According to the differential drive, only pixels that are to be changedare rewritten, such that the power would not be wastefully consumed.Also, when a display image is to be changed, the differential drive isexecuted only when the variable Count is less than the threshold valueTh1, such that an afterimage originated from an outline would not becomeconspicuous. Furthermore, there are other advantages in the differentialdrive. Fewer driving steps are executed, compared to the refresh drive,such that the differential drive is faster, and at least a part of thepixels turns to a black state and another part of the pixels turns to awhite state, such that flickers are more difficult to be recognized bythe observer, compared to the refresh drive.

In this manner, according to the present embodiment, when a changeoccurs in the display content on the display unit 10, if the integratedvalue obtained by counting sections where white pixels and black pixelsare placed next to each other since the last refresh drive exceeds thethreshold value Th1, the refresh drive is executed, and if theintegrated value is less than the threshold value Th1, the differentialdrive is executed. Therefore, in accordance with the present embodiment,high-quality display with reduced afterimage and lower power consumptioncan both be accomplished. Furthermore, high-speed display switching canbe achieved, which is effective in reducing flickers.

The first embodiment is configured in a manner that the main flow shownin FIG. 4 is executed with a change in display contents as a trigger,but may be configured in a manner that the main flow is executed at apredetermined time interval. In such a configuration, when the variableCount exceeds the threshold value Th1, the refresh drive is executed,but the same image is written even after the refresh drive has beenexecuted.

Second Embodiment

In the first embodiment described above, when the integrated value ofcounted sections where white pixels and black pixels are placed next toeach other since the last refresh drive exceeds the threshold value Th1,a refresh drive is executed. For this reason, when changes occurmultiple times in the display content, and the integrated value is lessthan the threshold value Th1, the refresh drive will not be executed. Inthis case, if the state in which white pixels and black pixels areplaced next to each other at the same locations appears each time thedisplay content is changed, afterimages remain at the same locations,and therefore their influence is believed to be small. However, in thefirst embodiment, if white pixels and black pixels are placed next toeach other multiple times at the same locations, these locations arecounted repeatedly, and there is a possibility that refresh drives maybe frequently executed, which leaves room for improvement.

The second embodiment that improves the aspect discussed above will bedescribed. An electro-optical device in accordance with the secondembodiment includes the outline detection process whose content inaccordance with the first embodiment (step Sa7 in FIG. 4 and FIG. 5) ismodified. Also, in the step Sa5 in the main flow (see FIG. 4), thevariable Count is reset to zero, and all boundary flags are also resetto zero. The boundary flags are flags that are provided for boundariesbetween pixels 20 arranged in a matrix of m rows×n columns, and each ofthe flags indicates as to whether or not two pixels sandwiching aboundary have become white color and black color, and the boundary hasbecome an outline portion since the last refresh drive up to the presentmoment.

FIG. 11 is a flow chart showing the outline detection process inaccordance with the second embodiment. First, in step Sc1, the generalcontrol unit 62 sets the target pixel at the 1^(st) row and the 1^(st)column. Then, in step Sc2, the general control unit 62 reads, from amongthe first VRAM 51, the pixel value of the target pixel and the pixelvalue of a next pixel located on the right of the target pixel, andjudges as to whether or not the exclusive OR (Xor) of the two pixelvalues is “1.” If the judgment result is “No,” both of the pixels are inthe same color of white or black, and therefore do not form an outline.Therefore, the process skips to step Sc6 to be discussed later. On theother hand, if the judgment result is “Yes,” one of the two pixels iswhite and the other is black, thereby forming an outline.

Therefore, in step Sc3, the general control unit 62 judges as to whetheror not the boundary flag corresponding to the right side next to thetarget pixel is “0.” If the judgment result is “No,” the process skipsto step Sc6 to be discussed later. On the other hand, if the judgmentresult is “Yes,” the general control unit 62 sets, in step Sc4, theboundary flag corresponding to the right side next to the target pixelto “1.” Here, the boundary flag corresponding to the right side next tothe target pixel was reset to zero immediately after the last refreshdrive (step Sa4), and would not be set to “1” other than in step Sc4.Therefore, when the judgment results in step Sc2 and the step Sc3 areboth “Yes,” it means that the target pixel and the next pixel on theright have formed an outline portion of an image for the first timesince the last refresh drive until the current judgment. Therefore, inthis case, in step Sc5, the general control unit 62 increments thevariable Count by “1.”

It is noted that there are two cases in which the variable Count isincremented in the step Sc5 as follows. As shown in FIG. 13A, the firstcase is where the pixel value of the target pixel is “1,” the pixelvalue of a next pixel on the right is “0,” and the boundary flagcorresponding to the right side next to the target pixel has been “0.”As shown in FIG. 13B, the second case is where the pixel value of thetarget pixel is “0,” the pixel value of a next pixel on the right is“1,” and the boundary flag corresponding to the right side next to thetarget pixel has been “0.” Also, even if the target pixel and the nextpixel on the right form an outline portion of an image again after theboundary flag corresponding to the right side next to the target pixelis set to “1” before the next refresh drive is executed, the judgmentresult in the step Sc3 becomes “No” such that the increment process inthe step Sc5 is skipped. For this reason, even when the same sectionforms an outline, the variable Count would not be counted repeatedly.

A similar judgment operation is also executed for a pixel located belownext to the target pixel. In other words, in step Sc6, the generalcontrol unit 62 reads, from among the first VRAM 51, the pixel value ofthe target pixel and the pixel value of a pixel located below next tothe target pixel, and judges as to whether or not the exclusive OR (Xor)of the two pixel values is “1.” If the judgment result is “No,” theprocess skips to step Sc10 to be discussed later. On the other hand, ifthe judgment result is “Yes,” the general control unit 62 judges in stepSc7 as to whether or not the boundary flag corresponding to the lowerside next to the target pixel is “0.” If the judgment result is “No,”the process skips to step Sc10. On the other hand, if the judgmentresult is “Yes,” the general control unit 62 sets, in step Sc8, theboundary flag corresponding to the lower side next to the target pixelto “1.” When the judgment results in step Sc6 and the step Sc7 are both“Yes,” it means that the target pixel and the next pixel below haveformed an outline portion of an image for the first time since the lastrefresh drive until now. Therefore, in this case, in step Sc9, thegeneral control unit 62 increments the variable Count by “1.”

It is noted that there are two cases in which the variable Count isincremented in the step Sc9 as follows. As shown in FIG. 13C, the firstcase is where the pixel value of the target pixel is “1,” the pixelvalue of a next pixel below is “0,” and the boundary flag correspondingto the lower side next to the target pixel has been “0.” As shown inFIG. 13D, the second case is where the pixel value of the target pixelis “0,” the pixel value of a next pixel below is “1,” and the boundaryflag corresponding to the lower side next to the target pixel has been“0.” Also, even if the target pixel and the next pixel below form anoutline portion of an image again after the boundary flag correspondingto the lower side next to the target pixel is set to “1” before the nextrefresh drive is executed, the judgment result in the step Sc7 becomes“No” such that the increment process in the step Sc9 is skipped. Forthis reason, even when the same section forms an outline, the variableCount would not be counted repeatedly.

In step Sc10, the general control unit 62 judges as to whether or notthe target pixel at the present time is at the m^(-th) row and then^(-th) column. When the judgment result is “No,” the general controlunit 62 shifts, in step Sc11, the target pixel to the next pixel on theright. Only when it is at the last n^(-th) column, the target pixel isshifted to a pixel located in the next row below at the first column.Then, the process returns to step Sb2. On the other hand, when thejudgment result in step Sb10 is “Yes,” it means that the variable Counthas been counted for sections which have formed outlines for the firsttime since the previous refresh drive, and therefore the outlinedetection process ends.

According to the second embodiment, when changes occur in the displaycontent of the display unit 10, the variable Count is counted only whenwhite pixels and black pixels are placed next to each other for thefirst time since the last refresh drive. If the variable Count exceedsthe threshold value Th1, a refresh drive is executed, and if it is lessthan the threshold value Th1, a differential drive is executed.Therefore, according to the second embodiment, it is possible to improvethe situation of frequently executing refresh drives.

Third Embodiment

The cause of afterimages described above will be once again examined.When a white pixel and a black pixel are placed next to each other, theelectric field on one of the pixels influences the other pixel, andtherefore an afterimage is supposed to be generated at this moment.However, as long as the state in which the white pixel and the blackpixel are next to each other is visually recognized in an emphasizedmanner, it is thought that the afterimage that is supposed to beoccurring would in effect not be conspicuous. In other words, theafterimage becomes conspicuous not when the white pixel and the blackpixel are placed next to each other, but when the two pixels indifferent colors placed next to each other transfer to the same color,and a color (afterimage) different from the color after transfer wouldexist, which is thought to make the afterimage conspicuous. In the firstembodiment described above, occurrences in which white pixels and blackpixels are placed next to each other are added up, while, in the secondembodiment, occurrences in which white pixels and black pixels areplaced next to each other for the first time since the last refreshdrive are added up, and when the integrated value (the variable Count)exceeds the threshold value Th1, the refresh drive is executed.Therefore, in accordance with the first embodiment or the secondembodiment, there is still a possibility of executing refresh driveseven when afterimages are not so conspicuous, which still leaves roomfor improvement.

Next, a third embodiment which improves the aspect described above willbe described. An aspect of an electro-optical device in accordance withthe third embodiment may be summarized as follows. When there is asection where two mutually adjacent pixels switch to the same color dueto a change in the display content, and one of the pixels is a whitepixel and the other is a black pixel in the state before the change ismade, such a section is considered to cause an afterimage to beconspicuous due to the change, and the variable Count is counted forsuch a section. It is noted that the third embodiment includes theoutline detection process whose content in accordance with the firstembodiment is modified, like the second embodiment. Also, in the stepSa5 in the main flow (see FIG. 4), the variable Count is reset to zero,and all boundary flags are also reset to zero, which are generally thesame as the second embodiment.

FIG. 14 and FIG. 15 are flow charts showing an outline detection processin accordance with the third embodiment. First, in step Sd1, the generalcontrol unit 62 sets the target pixel at the Pt row and the Pt column.Then, in step Sd2, the general control unit 62 reads, from among thefirst VRAM 51, the pixel value of the target pixel and the pixel valueof a pixel located next on the right of the target pixel, and judges asto whether or not the exclusive OR (Xor) of the two pixel values is “0.”If the judgment result is “No,” which indicates that both of the pixelsare in different colors, the process skips to step Sd5 to be discussedlater. On the other hand, if the judgment result is “Yes,” thisindicates that both of the pixels are in the same color in white orblack. Therefore, in step Sd3, the general control unit 62 furtherjudges as to whether or not a boundary flag corresponding to the sectionon the right side of the target pixel is “1.”

The boundary flag in the third embodiment is slightly different indefinition from that of the second embodiment. Specifically, theboundary flag in the third embodiment is similar to the secondembodiment in that it is provided at a section corresponding to aboundary between pixels, but different from the second embodiment inthat a boundary flag that is once set at “1” after having been reset tozero at the last reset drive may be reset again to “0.” Simply put, whenthe boundary flag in accordance with the third embodiment is “1,” itindicates that, in the state before the display content is changed, oneof the two pixels interposing the boundary is white, and the other isblack. For this reason, when the judgment results in the steps Sd2 andSd3 are both “Yes,” the target pixel and the pixel on the right mutuallyturn to the same color due to a change in the display content, and oneof them is a white pixel and the other is a black pixel in the statebefore the change is made. Therefore, in this case, in step Sd4, thegeneral control unit 62 increments the variable Count by “1.”

It is noted that there are four cases in which the variable Count isincremented in the step Sd4 as follows. As shown in FIG. 16A, the firstcase is where the pixel value of the target pixel is changed from “0” to“1,” and the pixel value of a next pixel on the right is not changedfrom “1.” As shown in FIG. 16B, the second case is where the pixel valueof the target pixel is not changed from “1,” and the pixel value of anext pixel on the right is changed from “0” to “1.” As shown in FIG.16C, the third case is where the pixel value of the target pixel ischanged from “1” to “0,” and the pixel value of a next pixel on theright is not changed from “0.” As shown in FIG. 16D, the fourth case iswhere the pixel value of the target pixel is not changed from “0,” andthe pixel value of a next pixel on the right is changed from “1” to “0.”In each of the four cases, the boundary flag corresponding to a sectionnext on the right of the target pixel is “1.”

Then, the general control unit 62 executes a process to reflect thestate of the current target pixel and the next pixel on the right to aboundary flag corresponding to a section on the right next to the targetpixel, to be ready for the next execution of the step Sd3 for the samesection. This process corresponds to steps Sd5-Sd7. More specifically,the general control unit 62 judges as to whether or not the exclusive OR(Xor) of the pixel value of the target pixel and the pixel value of thenext pixel on the right is “1” (step Sd5). If the judgment result is“Yes,” the general control unit 62 sets “1” at the boundary flagcorresponding to a section on the right next to the target pixel (stepSd6), and resets it to “0” when the judgment result is “No” (step Sd7).

A similar operation is also executed for a pixel located below next tothe target pixel. More specifically, in step Sd8 of FIG. 15, the generalcontrol unit 62 reads, from among the first VRAM 51, the pixel value ofthe target pixel and the pixel value of a pixel located below next tothe target pixel, and judges as to whether or not the exclusive OR (Xor)of the two pixel values is “0.” If the judgment result is “No,” theprocess skips to step Sd11. On the other hand, if the judgment result is“Yes,” the general control unit 62 further judges in step Sd9 as towhether or not the boundary flag corresponding to the lower side next tothe target pixel is “1.”

When the judgment results in steps Sd8 and Sd9 are both “Yes,” it meansthat the target pixel and the next pixel below mutually turn to the samecolor due to a change in the display content, and one of them is a whitepixel and the other is a black pixel in the state before the change ismade. Therefore, in this case, in step Sd10, the general control unit 62increments the variable Count by “1.”

It is noted that there are also four cases in which the variable Countis incremented in the step Sd10 as follows. As shown in FIG. 16E, thefirst case is where the pixel value of the target pixel is changed from“0” to “1,” and the pixel value of a next pixel below is not changedfrom “1.” Second, as shown in FIG. 16F, the second case is where thepixel value of the target pixel is not changed from “1,” and the pixelvalue of a next pixel below is changed from “0” to “1.” As shown in FIG.16G, the third case is where the pixel value of the target pixel ischanged from “1” to “0,” and the pixel value of a next pixel below isnot changed from “0.” As shown in FIG. 16H, the fourth case is where thepixel value of the target pixel is not changed from “0,” and the pixelvalue of a next pixel below is changed from “1” to “0.” In each of thefour cases, the boundary flag corresponding to a section below next tothe target pixel is “1.”

Then, to be ready for the next execution of the step Sd9 for the samesection, the general control unit 62 judges as to whether or not theexclusive OR (Xor) of the pixel value of the target pixel and the pixelvalue of the next pixel below is “1” (step Sd11). If the judgment resultis “Yes,” the general control unit 62 sets “1” at the boundary flagcorresponding to a section below next to the target pixel (step Sd12),and resets it to “0” when the judgment result is “No” (step Sd13).

In step Sd14, the general control unit 62 judges as to whether or notthe target pixel at the present time is at the m^(-th) row and then^(-th) column. When the judgment result is “No,” the general controlunit 62 shifts, in step Sd15, the target pixel to a next pixel on theright. Only when it is at the last n^(-th) column, the target pixel isshifted to a pixel located in the next row below at the first column.Then, the process returns to step Sd2 in FIG. 14. On the other hand,when the judgment result in step Sd14 is “Yes,” the outline detectionprocess ends.

According to the third embodiment, when a change occurs in the displaycontent, the variable Count is counted for only a section where adjacenttwo pixels mutually turn to the same color due to the change, and thetwo pixels in the state prior to the change form an outline. If thevariable Count exceeds the threshold value Th1, a refresh drive isexecuted. If the variable Count is less than the threshold value Th1, adifferential drive is executed. Therefore, according to the thirdembodiment, the condition in which a refresh drive is executed eventhough an afterimage is not so conspicuous can be improved.

Application and Modification

The invention is not limited to the embodiments described above, and thefollowing applications and modifications are possible. As shown in FIG.17, in a region 100 a, such as, a text box in the display region 100,each time a character or a mark is inputted, a change occurs in itsdisplay content. Similarly, in a region 100 c in which a cursor 100 b isexpected to be shifted, each time the cursor 100 b is instructed toshift, a change occurs in the display content. Because an outlineafterimage occurs with a change in the display content as a trigger,there is a higher possibility that afterimages occur in a concentratedmanner in a region where the display content is frequently changed.Accordingly, the display region 100 may be divided into a plurality ofregions. The extraction function, the counting function and the judgmentfunction may be executed for each of the divided regions, and a refreshdrive may be executed for only pixels included in a divided region wherethe variable Count exceeds the threshold value Th1. By thisconfiguration, the pixels that are subjected to a refresh drive arelimited, whereby the power consumption can be suppressed, andafterimages that may occur in a concentrated manner can be effectivelyreduced. Also, the region to be refresh-driven can be suppressed to thenecessity minimum, such that flickers can be better suppressed, comparedto the case where the entire display region 100 is refresh-driven. It isnoted that the threshold value Th1 in this instance may be set accordingto the number of pixels included in each corresponding one of thedivided regions. If there are any regions where the display content isnot changed, such regions may be configured such that the extractionfunction, the counting function and the judgment function are notexecuted.

Further, in each of the embodiments, the display unit 10 displays binaryvalues of white color and black color, but may be provided with ahalf-tone display capability. Even in the case of displaying half-tones,when an outline is formed by adjacent pixels having mutually differentgradations, the electric field on one of the pixels influences the otherpixel, which is thought to generate a similar afterimage. Whendisplaying half-tones, one of the conditions for a section to beextracted as forming an outline, a difference between pixel values(gradation values, gradation levels) of two pixels may be used forjudgment. Let us consider a case where, for example, the gradationlevels are defined sequentially by means of brightness levels asblack<dark gray<slightly dark gray<slightly light gray<light gray<white.In this case, when there is a great difference between two gradationvalues, for example, when a black or dark gray pixel is placed next to awhite or light gray pixel, the influence of the electric field isgreater, and therefore the variable Count may be incremented. On theother hand, when there is a small difference between two gradationvalues, for example, when a slightly dark gray pixel is placed next to aslightly light gray pixel, the influence of the electric field issmaller, and therefore the variable Count may not be incremented, or thevariable Count may be incremented once for each plural sections. On theother hand, when pixels closer in gradation to black color appear in awhite background, in particular, afterimages would more readily bevisually recognized. In this case, the variable Count may be morepreferentially incremented (by increasing the frequency of incrementactions),

Further, in each of the embodiments described above, the outlineextraction function, the counting function and the integrated valuejudgment function for a target pixel and an object pixel (an adjacentpixel on the right or an adjacent pixel below) are executed by thecontroller 60. However, an image to be displayed on the display unit 10is specified by the control of the CPU that is an external device. Forthis reason, these functions may be executed by the CPU, or by apersonal computer that is a host apparatus, and the controller 60 may beconfigured to control refresh drives and differential drives at thedisplay unit 10 based on the results of these functions.

In each of the embodiments, a refresh drive or a differential drive isexecuted after extracting an outline between a target pixel and anobject pixel. However, the invention is not limited to thisconfiguration. For example, in a drive system in which, whether or notdriving of each of the pixels is started is judged at each frame, and animage in each frame is updated, whether or not the variable Countexceeds the threshold value Th may be judged at each frame. If thevariable Count exceeds the threshold value Th, the update in the framemay be interrupted, and driving of the pixels may be stopped.Thereafter, a refresh drive may be executed.

Also, the shape of each pixel electrode is not limited to a square or arectangle, and may be a polygonal shape or a circular shape. Also, pixelelectrodes may be segment electrodes in various shapes including 7segment-shapes. When segment electrodes are used, for example, a dataline may be directly connected to each of the segment electrodes, andthe potential on each of the segment electrodes (pixel electrodes) maybe controlled by the potential on each of the data lines. Even in thesecases, sections where pixel electrodes with different gradations areplaced next to each other may be counted, and whether or not thevariable Count exceeds the threshold value Th may be judged. By this,effects similar to those of each of the embodiments described above canbe obtained.

Each of the embodiments has been described, using a mode including stepsof rewriting the entire pixels included in a predetermined region wherean outline is to be extracted to a single gradation as an example of therefresh drive. However, the refresh drive is not limited to such a mode.For example, when an image A is displayed succeeding a refresh drive,the refresh drive may be in a mode including a first step of displayinga gradation-inverted image of the image A, and a second step ofdisplaying the image A after the first step. Also in this case, therefresh step includes steps of rewriting pixels corresponding tosections counted in the outline extraction process (in other words,target pixels and object pixels with different gradations placed next toeach other) to a single gradation, such that afterimages can be erased.Also, the refresh drive may have another mode that includes rewritingpixels corresponding to sections counted in the outline extractionprocess (in other words, target pixels and object pixels with differentgradations placed next to each other) to at least a single gradation.Also in this case, afterimages can be erased by refresh drives.

Electronic Apparatus

Next, examples of electronic apparatuses using an electro-optical devicein accordance with any one of the embodiments described above will bedescribed. FIG. 18A is a perspective view of an electronic book readerusing the electro-optical device. The electronic book reader 100 isequipped with a book-shaped frame 1001, a cover 1002 provided in amanner freely opened and closed with respect to the frame 1001, anoperation unit 1003, and an electro-optical device in accordance withany one of the embodiments described above. It is noted that, in thefigure, only the display region 100 of the electro-optical device isexposed. With the electronic book reader 1000, contents of an electronicbook are displayed in the display region 100, and pages of theelectronic book can be turned by operating the operation unit 1003.Further, FIG. 18B is a perspective view of a wrist watch 110 using anelectro-optical device in accordance with any one of the embodimentsdescribed above. The wrist watch 1100 is equipped with theelectro-optical device in accordance with any one of the embodimentsdescribed above, and only its display region 100 is exposed. In thewrist watch 110, time, year, month and day are displayed in the displayregion 100. In addition to the above, other electronic apparatuses towhich an electro-optical device in accordance with any one of theembodiments described above is applicable includes electronic paper,electronic notebooks, calculators, cellular phones and the like.

The entire disclosure of Japanese Patent Application No. 2011-020762,filed Feb. 2, 2011 is expressly incorporated by reference herein.

1. A control device for controlling a display unit that includes pixels each having display elements, the control device comprising: a control unit counting sections where pixels with different gradations are placed next to each other in a predetermined region among an image to be displayed on the display unit, wherein the control unit outputs an instruction to execute a refresh drive in the predetermined region when an integrated value of the sections exceeds a predetermined value.
 2. A control device according to claim 1, wherein the control unit outputs an instruction to rewrite the entire pixels included in the predetermined region to a single gradation when the integrated value exceeds the predetermined value, then the control unit outputs an instruction to rewrite a part of pixels in the predetermined region to a gradation different from the single gradation.
 3. A control device according to claim 2, wherein the control unit outputs an instruction to rewrite pixels to be changed in the predetermined region when the integrated value equals to the predetermined value or less.
 4. A control device according to claim 1, comprising: an extraction function that extracts sections where pixels with different gradations are placed next to each other in the predetermined region, a counting function that counts the sections extracted by the extraction function, and a judging function that judges as to whether or not an integrated value provided by the counting function exceeds the predetermined value.
 5. A control device according to claim 4, wherein the extracting function extracts sections where pixels with different gradations are placed next to each other for the first time, after the last display of the pixels in the single gradation.
 6. A control device for controlling a display unit that includes pixels each having display elements, the control device comprising: a control unit counting sections where pixels with different gradations placed next to each other change to a single gradation in a predetermined region among an image to be displayed on the display unit, wherein the control unit outputting an instruction to execute a refresh drive in the predetermined region when an integrated value of the sections exceeds a predetermined value.
 7. A control device according to claim 1, wherein the predetermined region is composed of all or a part of the plurality of pixels in the display unit.
 8. A control device according to claim 6, wherein the predetermined region is composed of all or a part of the plurality of pixels in the display unit.
 9. A control device according to claim 1, wherein the refresh drive includes rewriting all of the pixels included in the predetermined region to a single gradation.
 10. A control device according to claim 6, wherein the refresh drive includes rewriting all of the pixels included in the predetermined region to a single gradation.
 11. An electro-optical device comprising: the display unit recited in claim 1; and the control device recited in claim
 1. 12. An electro-optical device comprising: the display unit recited in claim 6; and the control device recited in claim
 6. 13. An electro-optical device according to claim 11, wherein the refresh drive includes rewriting all of the pixels included in the predetermined region to a single gradation.
 14. An electro-optical device according to claim 12, wherein the refresh drive includes rewriting all of the pixels included in the predetermined region to a single gradation.
 15. An electronic apparatus comprising the electro-optical device recited in claim
 13. 16. An electronic apparatus comprising the electro-optical device recited in claim
 14. 